First check whether the chart uses overlapping categories, multiple selections, indexed data, or another denominator that explains the total.

Percentages do not always represent mutually exclusive shares. Treat the chart definition and footnotes as part of the exhibit, not decoration.

If categories overlap, say that the values should not be summed and interpret each percentage against its stated base.

Before calculating, restate what the denominator is. That one habit prevents many exhibit-reading errors.

What helped me was saying the assumption out loud in one sentence and then moving on. It made the reasoning easier to follow.

Small point, but I would also watch your pacing. When I rush this type of answer, I usually create a second problem.

For me, writing one short line before speaking helped a lot. It stopped me from over-explaining and made the answer cleaner.

ngl this is one of those things that feels bigger in prep than it does in the actual interview. A simple response is usually enough.